Increasing use is being made of labels produced by sophisticated techniques for the identification marking of parts of vehicles, machines, and electrical and electronic devices, etc., examples of such labels being identification plates, control labels for process operations, or guarantee badges or test badges.
In order to inscribe these plates or labels, use is widely made of powerful and controllable lasers which can “burn” markings, such as inscriptions, codes, and the like. High requirements are placed upon the material to be inscribed. For example, the inscription rate is to be high, the resolution capability is to be high, the application is to be simple, and the material is to have high resistance to mechanical, physical, and chemical effects. Commonly used materials, e.g. printed paper, electrolytically oxidized aluminum, lacquered aluminum, or PVC films, do not all fulfill these requirements.
The applicant is introducing a multilayer label which is self-supporting, and comprises a thin, opaquely pigmented lacquer layer over a thick lacquer layer, and is manufactured from an electron-beam-cured, solvent-free lacquer. A label of this type has been described in DE 81 30 861 U1. The label is inscribed by using a laser to engrave the thinner lacquer layer via layer ablation, thus revealing the lower, thicker lacquer layer. The chemical structure of the film material, and the electron-beam curing, gives the film material a high level of resistance.
Processing by means of a laser (preferably a Nd:YAG laser or a CO2 laser) makes it necessary that the upper lacquer layer serving as contrast layer be relatively thin (less than 15 μm), and that it must be of very constant thickness. This is achieved during the production process by using a precision applicator (multiroll system) to apply the thin lacquer layer. To this end, the thin lacquer layer is first applied to a process film or supportive backing film (polyester film), and a doctor is then used to apply the thick lacquer layer. Both lacquer layers are polymerized in a single operation via irradiation with electrons (80 kGy, 350 kV), thus producing a highly crosslinked polymer. This laser-lacquer film is then equipped with a self-adhesive mass, and is peeled away from the supportive backing film during the finishing process.
During the manufacture of the previously known laser-inscribable film, the application of the first lacquer coating is a costly and sensitive step of the process. For example, the precision applicator limits the working width, the selection of the lacquer colors is restricted, there is little flexibility available in coloring the thin lacquer layer, and an adequate quality of coating can be achieved only with a relatively low coating speed.
Furthermore, in some application sectors there is a desire for label individualization, which is to be in place before the laser-inscription process begins. By way of example, this type of individualization might comprise a customer-specific design. This, combined with a controlled distribution routing for the customer-specific individualized labels prior to inscription would serve to prevent counterfeiting, because it would then be almost impossible to forge inscribed labels.
It is an object of the invention to provide a process which can produce a laser-inscribable film and which can be carried out at lower cost than the previously known process, and which permits greater design freedom with respect to the laser-inscribable film, extending as far as customer-specific individualization.